<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<input type="text" id="input">
<button id="button">注册</button>
<script>
    function checkEmpty() {
        if (input.value.length === 0) {
            alert('不能为空');
            return false;
        } else {
            return true;
        }
    }
    function checkLength() {
        if (input.value.length < 6) {
            alert('长度不能小于6');
            return false;
        } else {
            return true;
        }
    }
    class Chain{
        constructor(fn) {
            this.fn = fn;
            this.next = null;
        }
        setNext(next) {
            this.next = next;
        }
        run() {
            let result = this.fn.apply(this, arguments);
            if (result === true && this.next !== null) {
                return this.next.run.apply(this.next, arguments);
            }
            return result;
        }
    }
    let chain1 = new Chain(checkEmpty);
    let chain2 = new Chain(checkLength);
    chain1.setNext(chain2);
    button.onclick = function () {
        chain1.run();
    }
</script>
</body>
</html>